1. Field of the Invention
This invention relates to a method for forming earth retaining walls, cut-off walls, and foundation piles in an earthen foundation or for forming a pillar in an earthen foundation for the purpose of foundation improvement.
2. Description of the Prior Art
In the past, a method for forming a pillar in an earthen foundation in which consolidating fluid spray nozzles which spray consolidating fluid horizontally are provided on an excavating shaft, consolidating fluid is sprayed horizontally from the consolidating fluid spray nozzles while excavating is executed by the excavating shaft, and the consolidating fluid and the soil of the original earthen foundation are stirred and mixed together was disclosed in Japanese Patent Publication [KOKOKU] No. 59-16049. In addition, a method for forming a pillar in an earthen foundation is also known in which an excavating shaft is positioned inside a casing tube, consolidating fluid spray nozzles which spray consolidating fluid horizontally are provided on said excavating shaft, the earthen foundation is excavated by the bit at the tip of the excavating shaft inside the casing tube, consolidating fluid is sprayed horizontally from the consolidating fluid spray nozzles, and the consolidating fluid and the soil of the original earthen foundation are stirred and mixed together inside the casing tube. In these examples of the prior art, because the consolidating fluid sprayed from the consolidating spray nozzles provided on the excavating shaft and the soil of the original earthen foundation are stirred and mixed together while the consolidating fluid is being sprayed horizontally, in addition to the soil of the original foundation being finely sheared by the consolidating fluid which is being sprayed horizontally, the consolidating fluid which is being sprayed horizontally revolves as a result of the rotation of the rotating shaft, and thus the finely sheared soil of the original foundation and the consolidation fluid are stirred and mixed together.
However, with either of the examples of the prior art described above, the rotating speed of the excavating shaft, the spray pressure from the consolidating fluid spray nozzles, and the penetration speed of the rotating shaft were set at fixed values regardless of the characteristics of the soil, such as clayish soil, sandy soil, etc. Because of this, such problems existed as differences in the soil causing the strength of the pillar formed in the foundation to be inconsistent, it not being possible to achieve high-quality foundation improvement, which is the objective, the consolidating fluid being supplied in greater amounts than needed, or excessive work time being required.
In addition, with a method in which the consolidating fluid is sprayed horizontally, although the method has the characteristics described above, because the stirring and mixing are accomplished within the range in which the consolidating fluid is sprayed while revolving, the stirring and mixing range for one rotation of the rotating shaft is an approximately circular shape, and in consideration of the viewpoint of achieving efficient stirring and mixing in accordance with the conditions of the earthen foundation and at such times as when the excavating shaft is ascending or descending, in some situations, horizontal spraying, or horizontal spaying alone, is not sufficient.
In consideration of the problems of the prior art described above, this invention proposes a method for forming a pillar in an earthen foundation, the first objective of which is to make it possible to form in an earthen foundation a high-quality foundation-improvement pillar by the most efficient method with respect to differences in the soil, and, in addition, the second objective of which is to make it possible to achieve the most efficient stirring and mixing together of the soil of the original foundation and the consolidating fluid in accordance with the conditions of the earthen foundation and the descent and ascent of the excavating shaft.